Pierre Gilieth [Jean Gabin] steps out of house #25 in a Paris street as curfew bells ring, moments after a tense night where he and his drunken girlfriend Jacqueline stumble into each other and he leaves a streak of blood on her dress. The scene shifts to Barcelona, where he peers through Venetian blinds while a detective quietly shadows him. In a smoky bar, Gilieth crosses paths with other French men who slyly lift his identifications and hand them to the detective, prompting a tense confrontation when the thiefs are discovered. He tries to fight back, but he repels the impulse to involve the police and instead keeps his trouble close.
With resources running low and rejection from a merchant ship leaving him stranded, Gilieth spots a recruitment placard for a unit of the Spanish Foreign Legion. The placard proclaims the era before the Spanish Civil War, bearing the markings of the Spanish Republic and the Law of 17 July 1934. Among the ranks, many enlist for survival—their pay a mere five Pesetas—yet the presence of Fernando Lucas [Robert Le Vigan] stands out for another reason. Lucas is Maneuvering with funds for cigarettes and barhopping, and his money seems mysteriously linked to his mother in the eyes of the other legionnaires, who assume he is deserting from the French Army. Gilieth grows wary when Lucas’s identification card slips into view, and Lucas quickly conceals it, prompting a cautious dance of suspicion between them. Gilieth, following the advice of his best friend Mulot [Raymond Aimos], attempts to read Lucas’s papers by pickpocketing him, but the effort fails.
To erase the sting of failure, Gilieth uses a newspaper clipping announcing a 50,000 Franc reward for the culprit behind the “Crime of Rue St-Vincent” and hands it to the base’s guards, hoping to dull the memory that gnaws at him. Lucas invites him for a drink, and the pair clash in a bar, where tempers flare and a fistfight erupts. The bandera—the unit’s marching group—finally moves south, and Gilieth begs his captain, Captain Weller [Pierre Renoir], to transfer Lucas away for overstepping personal boundaries. When the bandera departs, the Barcelona detective closes in on Lucas.
Mulot, ever the morale booster, leads Gilieth to a local joint with dancing girls to lift his spirits. It is there that Gilieth meets Aïscha el Saloui [Annabella], a native with distinctive marks on her forehead and chin, and he falls hard and fast for her. In a bold and emotionally charged moment, they marry in a gypsy ceremony, their forearms cut and their blood mingling as a ritual of union.
Plans to escape together to Rabat, among Aïscha’s people, take hold, but Gilieth recognizes that he must deal with Lucas first. He instructs Aïscha to feign devotion for Lucas and to entertain him, to buy time until Lucas’s true identity—his secrets—are revealed. Lucas presses Aïscha to leave Gilieth and become his own, and Gilieth confronts them both, demanding that Aïscha spit in Lucas’s eye as a test of loyalty. She complies and hands Lucas a keepsake coin, a token she hopes will survive any trouble that follows.
A heated confrontation between Lucas and Gilieth ends with a knife drawn, yet Gilieth spares Lucas’s life. In a stark confession, Lucas reveals he has a police badge and that he is not a true legionnaire. Captain Weller, enraged, orders him away, insisting that Lucas should quit if he survives, since he is not one of them. The heat-bleached desert air and the hot march of the troops push toward a final clash.
As the unit presses uphill toward a critical outpost, the sergeant’s orders are carried out and the bandera advances, while a fighter plane appears and some fall to “friendly fire” or to the unseen enemy. Captain Weller dies of heat exhaustion, leaving Gilieth and Lucas to shoulder the burden of command as the main force charges forward with machine guns blazing. In the climactic moment, Gilieth is struck by a sniper’s shot, and Lucas is forced to report the roll call: “Killed in action” for all of the twenty-four—except Gilieth, who is "Promoted on the battlefield to corporal and killed in action" and who is recorded as "Present" for the record.
With the battle won in memory, Gilieth returns to Aïscha and offers back her coin, explaining that he died thinking of her. The tragedy and the yearning for a life beyond the war haunt the closing frame, a stark meditation on loyalty, love, and the costs of choosing a path in the shadow of war.
